1. Field of the Invention
The invention is in the field of communications over power lines or the like.
2. Related Art
Communication of data via power lines includes the coupling of data encoded signals into and from the power lines. For various reasons, these data encoded signals are preferably on the order of 15 Volts (peak-to-peak) to achieve the maximum allowable Power Spectral Density (PSD) over the spectrum allowed by various standards and regulations. One approach to generating these 15 Volt signals includes using an amplifier to increase the signal from say approximately 2 Volts (peak-to-peak) to 15. This amplifier adds to the cost of a system because it requires an additional high voltage power supply sufficient to achieve the 15 Volts and is typically implemented on a separate silicon device, relative to the circuits used to generate the original signals, because of its higher voltage requirements. The 15 Volt signals are then coupled to a power line via a single low ratio isolation transformer.
In another approach, signals on the order of 15 Volts can be generated from signals on the order of 4 Volts peak-peak by using a single transformer with a high (e.g., 1:4) ratio of primary to secondary coils. This approach has the advantage that this same transformer may be used as an isolation transformer to couple the signals into the power line. This can result in significant savings. However, this approach presents several problems. For example, for a 1:4 (P:S) transformer the impedance seen before the transformer is 1/16th of the impedance seen after the transformer. This may result in impedance before the transformer that is difficult to drive. This low impedance also places requirements on any signal conditioning components between the signal source and the transformer. These requirements result in a greater component cost. Further, quality factors and parasitics associated with the windings and core of the transformer can limit the width of the frequency range over which the transformer will perform without loss in the resulting signal. As a result, if a wide frequency range is required with relatively high injected power capability, then very expensive or even impossible transformers may be needed.
Signal conditioning components are sometimes used to shape the frequency response of the driving signal, or to combine it with another signal in a different frequency band. It is important for optimum performance that these signal conditioning components are approximately the same impedance as the impedances driving and being driven by them to achieve maximum power efficiency. This can be difficult. There are many other signal conditioning functions, such as surge protection, impedance matching, and switching, that are not just passive but active, which require low loss components, this is more difficult to achieve if a low impedance is present due to a single high ratio transformer.